Seismic reflection analysis of the deeply buried Neoproterozoic rift basin beneath Sichuan Basin, southern China

The recent discovery of a giant gas field within the uppermost Neoproterozoic strata in the Sichuan Basin has motivated us to further investigate an underlying Neoproterozoic rift basin. Exploration in this deep-seated rift basin is currently lacking, and relevant wells are sparse. Therefore, this study analyzes the structure and evolution of the rift basin and characterizes the preliminary hydrocarbon conditions in this new and challenging exploration frontier. First, based on a systematic analysis of new magnetotelluric data and two-dimensional and three-dimensional seismic reflection data, rift-related faults are identified with predominately northeast-southwest strikes. The rift basin comprises a series of graben and horst structures with sedimentary successions thicker than 5 km. Rift-related faults were active before the Ediacaran (635 Ma), with mafic sills intruding the lower part of the rift basin along the surface of the basement or faults. Second, the evolution and deposits of the rift basin are extrapolated from integrated studies, including sparse well data, seismic reflection analysis, and the surrounding geology. The results show that this rift basin formed during 800-635 Ma and probably resulted from the breakup of Rodinia. The infill may represent a lower volcanic succession of the Banxi Group and an upper glacial succession of the Cryogenian. Finally, some positive conditions for hydrocarbon prospectivity are discussed. These findings can be used to develop strategies for deep hydrocarbon exploration in China and to provide an additional example of Neoproterozoic rift basins worldwide.